Historic Windows: UV and Thermal Transfer

Historic windows present challenges when it comes to mitigating the effects of UV and thermal transfer. Providing both UV and thermal barriers for historic windows is often accomplished via some ancillary attachment. Here are a few examples, with associated pros and cons:

Insulated roller shades- Can protect against UV while still allowing natural ventilation

- Can sometimes be concealed when not drawn (doesn't always interfere with historic import)- Not the best possbile air or thermal barrier - e.g., in winter, can still allow for condensation to form on glass

Sealed quilt or roman shade

- This refers to a heavier, well insulated interior shade mounted on tracks that forms a reasonably good air seal around the window- A well known brand is Window Quilt (claimed R value from 4.6 to 7.1)

- Bulky, and may not appeal to some; may detract from historic import- Better air/termal barrier than a roller shad, but might be less than adequate if both UV protection and natural ventilation are desired in summer

Exterior storm window- Might help to further mitigate any air/moisture infiltration issues- Newer ones are designed to be nearly invisible - don't detract from historic import- Can be onerous to remove every spring and replace every fall

Use of exterior awnings, overhangs, or plantings (transpiration, shade)- Natural, passive- Can help extend the effects of existing heating/cooling mechanisms

In general, what approaches have any of you attempted, and what sort of results have you achieved? What seems to be a preferred strategy (or combination of strategies), or potential best practice solution to this problem?

Replies to This Discussion

I did an audit recently for a lady that does custom window treatments. Curtains, blinds, drapes. She discussed the Hunter Douglas line of blinds that she handles. Interesting stuff. Some have an Energy Star Label, and make claims of an R-Value.

My personal preference is for Solar control outside the envelope. My professional guidance is that people have to do something and an effective interior solar control they will have installed and use is better than an approach that is not used or even installed.

Thanks very much Bill, for describing your exterior storm solution (sorry I'd neglected to reply when you first posted this a year ago). Question I have is: Do you drill weep holes in the bottom furring strip supporting the exterior storm? And if so, do you just leave them open or install small plugs and open or close when necessary? Thanks Bill!

I install the bottom furring strip in pieces and usually have enough left over from the other 3 sides to piece together the bottom. This is the only time I use that funky PVC wood. I keep the holes small, so I feel like it is OK to leave them open all the time. I haven't had any call backs yet, though sometimes I wonder if it is wise to claim that exterior storms will eliminate interior condensation problems.

Thank you so much for starting this group, my overarching passion is to merge the craftsmanship still intact in many older buildings with technology and building science.

I'd also like to add to your "laundry list" a product that I have had some experience/frustration with, but ultimately hope for. http://www.solarizewindowinsulators.com/ It's dang intriguing if nothing else. I'd love to hear of other folks' experiences with the Inflector product.

It's basically a reversable interior storm window-- radiant barrier on one side, solar absorber on the other. It's brilliant in concept but I can't help thinking it looks like an overpriced NASA-designed trash bag.

My mother in law had three skylights facing south in her 1890's home-office. She loved the light, hated the heat, and wanted to save energy in the winter too. (Wow, that's a lot to ask of a hole in your ceiling). So I installed three Inflector panels. She hated the way they looked and took them out before I ever got any good data on their performance. I'm a little suspicious of their own data claims, as the product is outside the realm of a SHGC-defined window/ storm tests.

Hi Chris. Thanks very much for added this to the forum. The information and test data they provide seems rather substantial. But I agree with you -- it'd be great to hear from any one else who's installed these or a similar reflective barrier, and had had a chance to observe the results. Agree that it at least sounds good.

Thanks very much for contributing all this information. It looks like a few of the links were broken when I tried them. In particular, the "Buy AEP -Kit" button is broken on both the Windo-Therm and AEP home pages and I couldn't find any other obvious links that worked. On the other hand, if you Google "Advanced Energy Panels Kit", quite a number of third parties who resell them are listed. Also, the Window-Therm and AEP home pages (one in the same) are either http://www.windotherm.com/ or http://www.advancedenergypanels.com/, respectively, while the R-Plus Window Insulators home page now seems to be http://rpluswindows.com/.

There's a company right in Boston that makes a very nice aluminum/low-e glass spring tension interior storm that I've seen a few times, who's name just keeps on eluding me. I need to sift though some paper files to find it (never an exciting prospect), but when I do, I'll post here as well.